# The mean weigt of 60 students is 40 kg. If the mean weight of boys is 50 kg, while that of girls is 30 kg. Find the numbers of boys and girls.

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by Coolaks

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by Coolaks

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Let the number of boys be 'x'

and girls in the school be 'y'.

therefore x + y = 60

since mean = sum of observations by no of observation

50*x + 30*y / x + y = 40

50x + 30y = 40*60

50x + 30y = 2400

5x + 3y = 2400/10 = 240

so we have 5x + 3y = 240 and x + y = 60

multiplying second equation by 3 , we get ,

5x + 3y =240

3x + 3y = 180

by subtracting , y terms will be cancelled , and

2x = 60

x = 30

substituting x in 2nd equation , we get,

30 + y = 60

y = 60 - 30 = 30

hence x = 30 and y = 30

and girls in the school be 'y'.

therefore x + y = 60

since mean = sum of observations by no of observation

50*x + 30*y / x + y = 40

50x + 30y = 40*60

50x + 30y = 2400

5x + 3y = 2400/10 = 240

so we have 5x + 3y = 240 and x + y = 60

multiplying second equation by 3 , we get ,

5x + 3y =240

3x + 3y = 180

by subtracting , y terms will be cancelled , and

2x = 60

x = 30

substituting x in 2nd equation , we get,

30 + y = 60

y = 60 - 30 = 30

hence x = 30 and y = 30